黏性土填料下考虑土拱效应的挡土墙被动土压力计算

为解释挡土墙后填土被动土压力的非线性分布现象,在考虑土拱形状为圆弧,滑裂面采用朗肯滑裂面的基础上,给出考虑土拱效应的被动土压力系数Kawn,进而基于应力状态法及土楔形体静力平衡两种思想求解了竖向平均应力 公式,在该基础上,给出黏性土填料下的挡土墙被动土压力分布公式、合力公式及作用点高度计算公式。通过与试验与其他方法对比,文中提出的方法得到验证。最后,研究了黏性土填料下的挡土墙被动土压力变化规律,即考虑土拱效应求得的黏性土填料的被动土压力分布呈现上小下大的指数型分布。此外,随着δ/φ（δ为墙土摩擦角,φ为内摩擦角）的增大,土拱效应逐渐增强,土压力合力点逐渐降低。     

两刚性圆球间双黏度流体挤压流动压力分析

颗粒物质是大量固体颗粒相互作用而组成的复杂体系。颗粒间孔隙水具有复杂连通结构和复杂的流动规律,直接影响颗粒体系的变形和强度,目前颗粒间隙液体的挤压流动和剪切运动分析是流体力学的难点。基于Reynolds润滑理论,导出了存在填隙双黏度流体时,两刚性圆球间流体的挤压流动速度场和压力方程。根据应力的变化情况,将流体分为屈服区和未屈服区,讨论了两区厚度与流体及颗粒参数的关系,分析了流体压力分布随计算参数的变化规律,得到了法向挤压黏性力的积分表达式,并给出了黏性力随不同参数的变化规律。     

The variability of critical shear stress, friction angle, and grain protrusion in water-worked sediments

The erodibility of a grain on a rough bed is controlled by, among other factors, its relative projection above the mean bed, its exposure relative to upstream grains, and its friction angle. Here we report direct measurements of friction angles, grain projection and exposure, and small-scale topographic structure on a variety of water-worked mixed-grain sediment surfaces. Using a simple analytical model of the force balance on individual grains, we calculate the distribution of critical shear stress for idealized spherical grains on the measured bed topography. The friction angle, projection, and exposure of single grain sizes vary widely from point to point within a given bed surface; the variability within a single surface often exceeds the difference between the mean values of disparate surfaces. As a result, the critical shear stress for a given grain size on a sediment surface is characterized by a probability distribution, rather than a single value. On a given bed, the crtitical shear stress distributions of different grain sizes have similar lower bounds, but above their lower tails they diverge rapidly, with smaller grains having substantially higher median critical shear stresses. Large numbers of fines, trapp.ed within pockets on the bed or shielded by upstream grains, are effectively lost to the flow. Our calculations suggest that critical shear stress, as conventionally measured, is defined by the most erodible grains, entrained during transient shear stress excursions associated with the turbulent flow; this implies a physical basis for the indeterminacy of initial motion. These observations suggest that transport rate/shear stress relationships may be controlled, in part, by the increasing numbers of grains that become available for entrainment as mean shear stress increases. They also suggest that bed textures and grain size distributions may be controlled, within the constraints of an imposed shear stress and sediment supply regime, by the influence of each size fraction on the erodibility of other grain sizes present on the bed.     

RB模式下砂土非极限主动土压力的离散元模拟与理论研究

针对刚性挡土墙绕墙底向外位移(RB)模式下砂土非极限主动土压力分布问题,采用离散元数值模拟对砂土的主动破坏过程进行分析。研究结果表明,非极限主动状态下,不同深度处土体内摩擦角变成极限值时,该点所需的水平位移近似相同,约为0.03%H,墙-土摩擦角至极限值时该点所需的水平位移S_δ近似与深度z呈线性关系,即S_δ=0.12%z;挡墙位移过程中,墙后土体中存在多个相互平行的“准滑动面”。根据模拟结果,在Liu提出的摩擦角调动值计算公式基础上进行了修正,并利用斜微分单元法,取墙后土楔体中平行于滑动面的薄层作为斜微分单元,建立了非极限主动状态下单元体静力平衡方程,得到了RB模式下挡墙不同位移量时非极限主动土压力计算公式。将计算结果与模拟结果和模型试验实测数据进行对比,验证了理论公式的合理性。     

A new approach to the equation of state of silicate melts: An application of the theory of hard sphere mixtures

A comparison of compressional properties of silicate solids, glasses, and liquids reveals the following fundamental differences: (1) Liquids have much smaller bulk moduli than solids and glasses and the bulk moduli of various silicate melts have a narrow range of values; (2) Liquids do not follow the Birch’s law of corresponding state as opposed to solids and glasses; (3) The Grüneisen parameter increases with increasing pressure for liquids but decreases for solids; (4) The radial distribution functions of liquids show that the interatomic distances in liquids do not change upon compression as much as solids do. The last observation indicates that the compression of silicate melts occurs mostly through the geometrical arrangement of various units whose sizes do not change much with compression, i.e., the entropic mechanism of compression plays a dominant role over the internal energy contribution. All of the other three observations listed above can be explained by this point of view. In order to account for the role of the entropic contribution, we propose a new equation of state for multi-component silicate melts based on the hard sphere mixture model of a liquid. We assign a hard sphere for each cation species that moves in the liquid freely except for the volume occupied by other spheres. The geometrical arrangement of these spheres gives the entropic contribution to compression, while the Columbic attraction between all ions provides the internal energy contribution to compression. We calibrate the equation of state using the experimental data on room-pressure density and room-pressure bulk modulus of liquids. The effective size of a hard sphere for each component in silicate melts is determined. The temperature and volume dependencies of sphere diameters are also included in the model in order to explain the experimental data especially the melt density data at high pressures. All compressional properties of a silicate melt can be calculated using the calibrated sphere diameters. This equation of state provides a unified explanation for most of compressional behaviors of silicate melts and the experimental observations cited above including the uniformly small bulk moduli of silicate melts as well as the pressure dependence of Grüneisen parameters. With additional data to better constrain the key parameters, this equation of state will serve as a first step toward the unified equation of state for silicate melts.     

Micro- and macro-behaviour of fluid flow through rock fractures: an experimental study

Microscopic and macroscopic behaviour of fluid flow through rough-walled rock fractures was experimentally investigated. Advanced microfluidic technology was introduced to examine the microscopic viscous and inertial effects of water flow through rock fractures in the vicinity of voids under different flow velocities, while the macroscopic behaviour of fracture flow was investigated by carrying out triaxial flow tests through fractured sandstone under confining stresses ranging from 0.5 to 3.0 MPa. The flow tests show that the microscopic inertial forces increase with the flow velocity with significant effects on the local flow pattern near the voids. With the increase in flow velocity, the deviation of the flow trajectories is reduced but small eddies appear inside the cavities. The results of the macroscopic flow tests show that the linear Darcy flow occurs for mated rock fractures due to small aperture, while a nonlinear deviation of the flow occurs at relatively high Reynolds numbers in non-mated rock fracture (Re?>?32). The microscopic experiments suggest that the pressure loss consumed by the eddies inside cavities could contribute to the nonlinear fluid flow behaviour through rock joints. It is found that such nonlinear flow behaviour is best matched with the quadratic-termed Forchheimer equation.     

对库仑土压力理论的若干修正

库仑土压力理论至今仍是计算土压力的重要方法而被人们所熟知。通过分析库仑土压力的墙后土楔体的受力特点,特别是深入研究了土楔体与墙的作用力关系,对库仑土压力理论给出了一些修正。认为土楔体和挡土墙之间的作用力（即定义的土压力）,并非一定要达到极限状态,所以不能确定土压力的作用方向,但土压力的作用方向必须在其允许的角度范围之内。所以,认为库仑主动土压力为作用方向角度变化范围内的最大值,库仑被动土压力为作用方向角度变化范围内的最小值。对于墙后土楔体,认为墙体和土楔体是两个不同物体,土楔体的形成是因为土中产生潜在破裂面,而原库仑土压力理论要求墙体与土之间也达到临界状态是不必要的。墙体对土楔体的作用力（即土压力）实质就是相当于一物（墙）施加于另一物（土楔体）的力,即使土楔体滑动了,两物之间也并非要滑动。推导了主动土压力计算公式,给出了被动土压力的近似计算方案。算例证明,计算结果与原库仑理论有明显不同。该研究对库仑土压力的修正和求解值得引起重视。     

Wave-induced stresses and pore pressures in sloping seabeds

By using the Mellin transform, a general solution is obtained for the total stresses and pore pressure distribution in an infinite wedge under fairly general conditions of loading. The results for the particular case in which each surface is subjected to static sinusoidal pressures are given in an explicit form. The infinite integrals can be evaluated by numerical integration methods. This analytical method is verified by different cases. The results of this study could be used to determine the total stresses and pore pressures induced by a wave on a sloping seabed.     

基于薄层单元法主动土压力计算的复合遗传算法

作用于挡土墙侧土压力的计算一直沿用经典的土压力理论,其土压力分布沿墙高呈直线分布,但实践证明它们与实际情况不符。在已有研究成果的基础上,为提高计算精度,假定挡土墙后土体潜在滑裂面为由对数螺线面和平面组合而成,根据挡土墙后土体薄层单元的极限平衡条件推导出土压力的计算公式。由于土压力计算值与滑裂面的位置有关,为寻找潜在最危险滑裂面,在简单遗传算法中引入复合形搜索法得到一种高效的复合形遗传算法,并将其用于墙后填土潜在最危险滑裂面搜索和相应主动土压力计算。最后,对室内模型挡墙和现场实际挡墙后填土土压力进行了分析计算,计算值与实测值吻合很好,这表明该方法不仅可行,而且可靠。     

Pseudo-dynamic methods for seismic passive earth pressure behind a cantilever retaining wall with inclined backfill

The designing of retaining walls requires the complete knowledge of earth pressure distribution. Under earthquake conditions the design needs special attention to reduce the devastating effect, but under seismic conditions, the available literature mostly uses the pseudo-static analytical solution as an approximate to the real dynamic nature of the complex problem. This paper shows a detailed study on the seismic passive earth thrust behind a cantilever retaining wall with inclined backfill surface by pseudo-dynamic analysis. A planar failure surface has been considered. The effect of variation of parameters such as soil friction angle, wall friction angle and back fill inclination have been explored. A complete analysis shows that the time dependent non-linear behaviour of the pressure distribution obtained in the present method results in more realistic design values of earth pressures under earthquake conditions. Results are provided in tabular and graphical non-dimensional form and compared thoroughly with the existing values in the literature.     

Reference of pressures in hydrogeology

This paper deals with the complex interrelations of regional tilt of the pressure surface, water temperature, density gas saturation, and pressures in determining the direction and rate of flow of water in different hydrologic depth zones. The various ideas of other Soviet authors are analyzed and evaluated. The author points out that the inequality method should not be used to test for flow in or between strata if the heights of reference points are similar or if the density is especially important in understanding long - time movements of occluded water in the so-called ”stagnation zone.“ — B.N. Cooper.     

An experimental study of single and two-phase fluid flow through fractured granite specimens

Triaxial tests on the two-phase flow of air and water through fractured granite specimens were performed to discover whether the two-phase fluid flow within rock fractures was laminar or turbulent. The two-phase flow characterization was carried out based on the macroscopic two-phase steady state flow model and the homogeneous steady state flow model. Rock specimens with a single natural fracture (joint roughness coefficient, JRC < 10) were tested using two-phase, high pressure triaxial rig. Experimental results show that the estimated Reynolds numbers for various inlet fluid pressures are well below 1000. The findings of this study reveal that both single and two-phase flow through rock fractures (JRC < 10) can be characterized as laminar flows at moderate inlet fluid pressures. However, for single-phase air flow, an increase in inlet air pressures may result in the formation of turbulent flow.     

应用Rankine理论的主动土压力计算

应用应力圆将Rankine理论计算主动土压力的方法延伸至坡面具有倾斜角的粘性填土，得出主动土压力强度沿墙背呈非线性分布的规律。根据填土倾斜角对填土内摩擦角的相对关系，导出土压力大小及作用点深度的计算公式，并绘制出曲线，以备查用。     

Chemistry and surface morphology of soil particles from Luna 20 LRL sample 22003

Six siliceous glass spheres, five siliceous glass-bonded agglutinates and one breccia fragment from Luna 20 LRL sample number 22003 were analyzed by optical microscope, scanning electron microscope, scanning electron microprobe and energy-dispersive techniques. The data suggest that most of the glass spheres were probably derived locally by meteoritic impact processes and that most craters on their surfaces may have occurred from impacts of relatively high velocity particles in the impact-produced debris cloud while the glass sphere was at elevated temperatures. This is suggested by the nature of the craters, the partially buried fragments of plagioclase surrounded by radiating fractures and by the apparent absence of craters on the glass surfaces of the glass-bonded agglutinates. One glass sphere has a surface suggestive of a complex multiple impact origin involving liquid siliceous material and numerous siliceous spherules from 0.1 μm to 1 μm in diameter that may have formed from vaporization and condensation processes possibly in a relatively large scale meteoritic impact event.The surfaces of the siliceous glass spheres have several different types of materials. Concentration of metallic iron spherules on the surfaces of the glass spheres is generally lower than for similar Apollo 11 and 12 glass spheres. This is consistent with reduction processes being of primary importance in the formation of this metallic iron. Surface material composed only of Ca, C and O₂, possibly CaCO₃, is probably derived from carbonaceous chondrites. Splashes of material rich in Ca, Al, Fe, K and Cl occur. The origin of the relatively low temperature chlorine-bearing melt is unknown but it may be related to vaporization and condensation processes, possibly volcanic in nature, or possibly to partial fusion of components of carbonaceous chondrites. Siliceous surface material rich in potassium may represent either fused splash material of granitic composition or material enriched by vaporization and condensation processes.     

刚性挡土墙主动土压力颗粒流模拟

将土体离散为具有滑动连接模型的刚性条块,用颗粒流PFC2D程序数值从细观力学角度模拟了墙体平移(T)、绕墙底转动(RB)和绕墙顶转动(RT)位移模式下不同位移大小时刚性挡土主动土压力分布。模拟结果表明：刚性挡墙主动土压力非线性分布、墙土间外摩擦角和土体剪切角或内摩擦角对土压力有很大影响;墙体绕顶部转动时,大约0.3倍墙高以上的主动土压力大于静止土压力产生土拱效应;模拟计算值与模型试验实测数据吻合比较好,具有一定的理论价值。     

不同粒度颗粒在非恒定管流中跟随性试验

管道中固液两相流水击对管道和输送系统可能产生严重的破坏,而固液两相在这种非恒定流中的运动特性是计算最大水击压力变化的重要依据。采用粒子图像测速技术（Particle Image Velocimetry,PIV）,通过试验研究水击发生时,水平圆管中不同平均流速、颗粒粒径条件下,流体介质和粗颗粒在管道断面的速度分布以及粗颗粒跟随性的变化规律。研究结果表明:①在水击发生的不同时刻,圆管流中粗颗粒的流速在管道断面分布呈不规则的抛物线型分布,主要表现为靠近管道壁面底部的颗粒流速略小于靠近管道顶部流速,当颗粒粒径大于1.5 mm,平均流速小于2.5 m/s时,粗颗粒表现出明显的沉降特性;②粗颗粒的跟随性与颗粒受力有密切关系,其中颗粒速度与流体速度的变化量是影响颗粒受力的重要参数;③基于试验数据拟合得到了水击条件下粗颗粒跟随性系数k的经验公式,并分析了颗粒粒径、管道直径、两相流平均流速以及水击发生时间等不同参数对粗颗粒跟随性系数的影响,公式计算值与实测值之间的误差在5%以内。     

人造多晶冰三轴压缩强度特性试验研究

为研究冰的三轴强度特性,对人造宏观各向同性冰进行了不同温度和不同围压下的恒定加载速率三轴压缩试验,得到多晶冰三轴压缩的应力-应变曲线、抗压强度与温度之间的关系,利用莫尔-库仑强度准则分析了温度和围压对强度参数的影响.结果表明：轴向应变加载速率为1.67×10-4 s-1时,不同温度、不同围压下冰的应力-应变曲线均为应变...     

Stability analysis of invariant points using Euler spheres, with an application to FMAS granulites

Alternative assignment of invariant point stabilities in a possible P – T  phase diagram is given by a family of grids that derives from a form of the Euler equation. Invariant points are represented by great circles that divide the surface of a sphere (the Euler sphere) into polygonal regions that correspond to the number of potential solutions or grids in n -component systems with n +3 non-degenerate phases. A particular invariant point is stable in all grids on one side of the great circle and metastable on the other. The advantage of this representation is the ease and efficiency by which all grids consistent with experimental and theoretical constraints can be identified. The method is well suited for systems of n +3 phases in which the thermochemical data necessary for direct calculation of the phase diagram is either uncertain or non-existent for one or more of the phases. The mass balance equations among the n +3 phases of interest define the Euler sphere for any particular system. There is a unique Euler sphere for unary systems, and another for binary systems. Ternary and quaternary systems have four and 11 different types of Euler spheres, respectively. In the ternary case with six phases, the 16 non-degenerate chemographies belong to four groups that are associated with the four Euler spheres. An analysis of those groups shows a close relationship between the topologies of the chemographies and the topologies of the grids represented on the Euler sphere. Euler spheres for degenerate chemographies are characterized by a smaller number of spherical polygons. A useful application of the Euler sphere concept is the systematic derivation of possible FMAS petrogenetic grids from subsystem constraints. Assumption of just one stable invariant point in each of MAS and FAS systems is consistent with seven FMAS grids involving cordierite, garnet, hypersthene, quartz, sapphirine, sillimanite and spinel.     

基于土拱效应原理求解挡土墙被动土压力

对平移模式下的刚性挡土墙和滑裂面间的楔形土体处于被动极限平衡状态的应力进行分析,考虑墙面和滑裂面之间土体水平力平衡,运用土拱效应原理推导出被动土压力系数和滑裂面水平倾角。并根据水平单元土体的静力平衡条件建立平衡方程,提出被动土压力分布、土压力合力及其作用位置的公式。将公式计算结果与试验结果以及库仑、朗肯理论所得结果进行比较,结果表明,与试验结果接近,验证了所得计算方法的合理性。     

挡土墙主动土压力的库仑统一解

基于极限平衡理论,视墙后填土为服从Mohr-Coulomb屈服准则的理想弹塑性材料,指出库仑土压力理论存在的一些缺陷,明确提出极限土压力是由墙后塑性土体产生,并假定塑性区的一族滑移线为直线,即平面滑裂面,建立了更为完善的滑楔分析模型,求解了在一般情况下考虑黏性土作用的挡土墙主动土压力、滑裂面土反力以及它们的分布,而经典库仑和朗肯主动土压力为其特例。